Thin-film electronic devices, such as organic light emitting diode (“OLED”) displays, have to be encapsulated against the ingress of reactive materials such as oxygen and water to ensure good operating and storage lifetime. When manufacturing OLED displays, the encapsulation portion of this process should be fast and provide a high yield of displays that are reliable and cost effective. To minimize cost, typically, multiple OLED displays are fabricated on a single large substrate and after encapsulation, the substrate is singulated to produce individual encapsulated OLED displays. To increase yield and reduce cost, the number of OLED displays fabricated on the substrate is as large as possible. However, the tight spacing of the OLED displays on the substrate causes difficulties in the encapsulation process.
FIG. 1 shows prior art multiple encapsulated OLED displays on a single substrate 103. OLED displays 118, 121, 124, 127, 130, 133, 136, 139, 142 are all on a substrate 106. The OLED display 118 includes an active area 109 on the substrate 106. The active area 109 includes columns of electrodes and rows of electrodes. The rows of electrodes are perpendicular to the columns of electrodes. An organic layer is between the columns of electrodes and the rows of electrodes. OLED pixels are formed at the intersections of the-columns of electrodes and the rows of electrodes. A perimeter seal glue 115 is deposited on the substrate 106 around the active area 109 so that an individual encapsulation lid 117 (e.g., a glass lid or a metal cap) can be glued to the substrate 106 in order to seal (e.g., encapsulate) the active area 109. The individual encapsulation lid 117 can contain a getter material in or on the lid. The getter material absorbs oxygen and/or moisture that is, for example, residual in the display package, or that, during display storage and operation, leaks through the perimeter seal glue 115 between the substrate 106 and the encapsulation lid 117. Conductive traces (not shown) are routed from the electrodes of the OLED display 118 to a contact pad 112. The contact pad 112 is used to couple the traces to a connector such as a flex connector. The connector is used, for example, to couple the display 103 to an external device such as a display driver (e.g., a row driver and a column driver). This encapsulation process of individually sealing each active area with a separate encapsulation lid is slow and costly. The precision needed to place each encapsulation lid over the active area, especially when the active areas are very close together, slows down the manufacturing process, reduces the yield because of unreliable displays due to not satisfying the increased precision needed, and increases the cost per display thus making this encapsulation process ineffective for mass producing multiple OLED displays.
An alternative technique is to encapsulate all of the active areas on the substrate at once by mating a cover sheet (e.g., the cover sheet can be a continuous sheet, i.e., foil) to the substrate where that encapsulation lid is the same size as the substrate. This alternative technique is shown in FIG. 2. FIG. 2 shows prior art multiple encapsulated OLED displays on a single substrate. OLED displays 156, 159, 162, 165, 168, 171, 174, 177, 180 are all on a substrate 154. The OLED display 118 includes an active area 183 on the substrate 154. A perimeter seal glue 189 is deposited on the substrate 154 around the active area 183. The perimeter seal glue is also deposited around the active areas of all of the other OLED displays. All of the active areas are encapsulated at once by mating a cover sheet that is the same size as the substrate 154 to the substrate 154 (the cover sheet is not shown in FIG. 2; the cover sheet can be, for example, a continuous sheet, i.e., foil). The mating occurs by pressing together the cover sheet and the substrate 154 and then curing the perimeter seal glue. After the cover sheet is mated with the substrate 154, the substrate 154 can be singulated along the singulation lines 192, 195, 198, 201, 204 by a scribe and break process, a cutting process, or a stamping process all of which are known in the prior art. The singulation of the substrate 154 yields individual OLED displays. Getter material can be attached to the cover sheet. Conductive traces (not shown) are routed from the electrodes of the OLED display 156 to a contact pad 186 that is used to couple the OLED display 156 to an external device.
This encapsulation process has several problems. One problem is that when the cover sheet and the substrate 154 are pressed together (this is typically done in inert atmosphere), the perimeter seal glue spreads and it becomes difficult to obtain a uniform bond line without bubbles, narrow openings, and meander structures. This difficulty is due, in part, to the pressure build-up between the cover sheet and the substrate 154 once both are close enough that the glue contacts them both but these two are further pressed together in hopes of producing a thin and uniform perimeter seal glue line around each active area. The pressure resulting from this further pressing together produces tiny openings or locally narrow sections in the perimeter seal glue line that then result in poorly encapsulated OLED displays. Some of the pressure building up on the perimeter seal glue is caused by gas pressure inside the areas enclosed by the perimeter seal glue between the substrate 154 and the cover sheet. Another problem is that the perimeter seal glue, upon being further pressed together, can spread over the singulation lines. This spreading of the glue over the singulation lines reduces encapsulation quality because, for example, an accurate scribe and break is more difficult and the yields are lower when the glue spreads over the singulation lines. The pressure between the substrate and the cover sheet are hard to control when mass producing multiple OLED displays thus resulting in poorly encapsulated displays due to perimeter seal glue lines that are nonuniform and have a thin width.
For the foregoing reasons, there exists a need to encapsulate thin-film electronic devices such that they can be quickly, reliably, and cost effectively mass produced while minimizing the reduction in encapsulation quality resulting from the high pressure applied to the perimeter seal glue.